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Apollo researcher David Carrier told me that he was asked what soil experiments the astronauts could perform, and he suggested that they take a picture of a bootprint. Therefore it was added to the activities for Buzz Aldrin to perform. He found an undisturbed spot on the surface, planted a boot cleanly, then stepped back and got the photo. The clean, vertical edges on the bootprint showed that lunar soil has high internal cohesions. It acts like damp soil, even though it is completely dry. This is because the soil is powdery and the gravity is low, so cohesion dominates over gravity on the sides of the bootprint. This was the first offworld granular mechanics experiment in human history.

Every photo taken by the Apollo astronauts was for scientific purposes--and yet some also had artistic, cultural and historic significance as well. In this particular case there is significant scientific information revealed by the photo. How deep is the soft regolith? What is its texture? Its density?